1. Field of the Invention
The present invention relates to an exposure apparatus and a device manufacturing method.
2. Description of the Related Art
In a semiconductor exposure apparatus that exposes a wafer (substrate) to a pattern of a reticle through a projection optical system, it is important to accurately align a surface of the wafer with an image plane of the projection optical system (i.e., focusing) for realizing miniaturization of a circuit pattern, and an increase in yield of production.
For example, Japanese Patent Laid-Open No. 6-260391 suggests a pre-reading focus measurement system, as a unit configured to accurately align a surface of a wafer with an image plane in a scanning exposure apparatus.
The focus measurement system includes a focus sensor that performs a focus measurement for a measurement point at a position apart from an exposure area of a projection optical system by a predetermined distance in a direction opposite to a scanning direction. Also, the focus measurement system measures the surface shape of a wafer by using the focus sensor before the measurement point enters the exposure area.
The focus sensor measures the position of the surface of the wafer in a direction parallel to an optical axis of the projection optical system by using a plurality of measurement points.
The surface of the wafer is aligned with the image plane on the basis of the measurement result, and focusing is performed.
In the above-mentioned focus measurement system suggested by Japanese Patent Laid-Open No. 6-260391, the focus measurement of a shot area on a substrate is started before the shot area reaches the exposure area.
Owing to this, a constant speed section in which a wafer stage is driven at a constant speed has to be provided before the shot area reaches the exposure area.
To reduce a time necessary for the exposure, or to increase the throughput, the constant speed section may be reduced, and the focus measurement may be performed even in an acceleration section in which the wafer stage is accelerated.
However, a deformation or a vibration is possibly generated at the wafer stage in the acceleration section, and hence, the accuracy of the focus measurement may be degraded.
Thus, it is difficult to increase the throughput by reducing a preparatory distance for performing a scanning exposure on the shot area.
In light of the above situations, it would be desirable to provide an exposure device that increases the throughput by reducing the preparatory distance.